Automatic sensitivity control for sound actuated detection and alarm systems



Nov. 3, 1964 H.' M. LARRICK ETAL 3,155,954

AUTOMATIC SENSITIVITY CONTROL FOR SOUND ACTUATED DETECTION AND ALARM SYSTEMS Filed June 15, 1962 LI L2 AI Fr L INVENTORS HOWARD M. LARRICK a WA TER R. BROSCH ATTORNE YS United States Patent AUTOMATIC SENSITIVITY CONTROL FGR SUUND AQTUATED DETECTION AND ALARM SYSTEMS Howwd M. lLarriclr, 3195 Howard Ave. NVL, Canton, Ohio, and Walter R. lllrosch, 2032 Gregg Road,

Akron 19, Ohio Filed June 15, 1962, der. No. 2%,763 1 Claim. (ill. 34%261) This application is a continuation-in-part of our copending US. application, Serial No. 4,791, filed January 26, 1960, now U.S. Patent No. 3,049,699.

The present invention relates generally to detection and alarm systems. More particularly, the present invention relates to alarm systems which are actuated by sounds or vibrations of a specific, predetermined amplitude. Specifically, the present invention relates to an alarm system which is capable of distinguishing between sounds of triggering amplitude created by environment and those created by intrusion.

Sound actuated detection and alarm systems respond to sound disturbances, referred to as intrusion sounds, which occur in the area or space under surveillance. Such sounds may result from glass breakage, pounding, jimmying, burning, etc. While it is desirable for the alarm system to be thus actuated by sounds of an unusual naturei.e., of a predetermined amplitudewhich are generally associated with disturbances resulting from the presence of unauthorized persons, it is equally as desirable for the detection alarm system to be nonresponsive to h aeatelsasaa WMWWW" 1 known d vices can be preset to remain unaffected by environmental sounds up to and including a predetermined amplitude, as, for example, the sound of motors, fans, or the like. However, these prior known soundactuated devices have not been able to discern between sporadic environmental sounds of triggering amplitude and intrusionsound's.

For example, rooms, areas, buildings or warehouses required to be furnished with alarm devices are often located adjacent railroads, super highways or airports. The passing of a train, truck or airplane in proximity to the location under surveillance produces sound waves of sufiiciently high amplitude and intensity to actuate the alarm system. To preset a sound actuated detection and alarm system to remain inactive to all sounds of the amplitude of these sporadic environmental sounds would render the system ineiiectual to far too great a range of intrusion sounds. i

It is therefore an object of the present invention to provide a sound-actuated detection and alarm system capable of distinguishing between sporadic environmental sounds of a far greater amplitude than required or" intrusion sounds to actuate the system.

It is a further object of the present invention to provide a system as above which is not self retriggered after once having been actuated.

It is a still further object of the present invention to provide an alarm system as above which may be set to give the operator an opportunity to leave the surveillance area without triggering the system.

These and other objects which will become apparent from the following specifications are accomplished by means hereinafter described and claimed.

3,,l55,954 Patented Nov. 3, 1964 One preferred embodiment of the present invention is shown by way of example in the accompanying drawings and described in detail without attempting to show all of the various modifications in which the invention might be embodied; the invention being measured by the append ed claim and not by the details of the specification.

The drawing is a schematic wiring diagram of the operative circuits of a sound-actuated detection and alarm system according to the present invention.

In general, a detection and alarm system according to the present invention comprises a microphone,or sound pickup means, which feeds into an amplifier means. An energizing circuit is actuated by said amplifier means to trigger a signaling device.

An automatic sensitivity control circuit monitors the signal being fed to the energizing circuit and, if it is of sporadic environmental origin, blocks the system from being actuated in response to that sound.

An amplification control circuit also compatibly operates with the automatic sensitivity control circuit to neg atively bias the amplifier in order to prevent echoes, or reverberations from the signaling device itself, from re-' triggering the system, and to block impulses from triggering the signaling mechanism when setting the system in order to give the operator an opportunity to leave the area being guarded.

The alarm system, indicated generally by the numeral 1%, may be self-contained in an enclosing case, indicated in schematic outline 11, which is portable for moving about fromplace to place and which need only beconnected to the usual alternating current service line, or, as will be seen, the system is readily adaptable as a fixed installation.

A microphone, or suitable transducer means 12, gencrates electrical signals in response to sound waves in the room or space under surveillance. The signals from the microphone pass through a filter 14 and are amplified by an amplifier 15. The amplified signals are fed from the output of the amplifier to a control apparatus 16, which, when the sigpglg a rg p g s gfijgipnt am p l gt ugg, acts to energize a loud speaker or other signahng device 17. Signals from additional or substitute sensing devices may be fed to the filter 14 through jacks J1 or J2 and auxiliary audible or visual signaling devices, sirens, blinkers and the like may be connected to the terminal leads'Al and A2.

The filter 14 functions to I frequencies or to de-emphasize others, so that the alarm device may be made more or less responsive to certain types of intrusion sounds. The filter 14 may be omitted where such specific response is not required, as it constitutes no part of the automatic sensitivity controlcircuit of the present invention. a

The amplifier 15 comprises a tube VT connected as a grounded. grid amplifier'and having the output of the -V2 and V3, through the resistors 21 and 22, are made to an automatic sensitivity control circuit and also to an amplification control circuit, the latter of which includes emphasize certain sound provide other adjustment means.

resistor 23, capacitor 24 and capacitor 25, and which applies the negative bias on the amplifier to render the amplifier insensitive to signals from the microphone for a predetermined interval immediately after setting the device and immediately after the device has been actuated by an intrusion sound. j

Direct current voltages are supplied to the amplifier 15 and to the control circuit 16 through a positive line 26 and a negative common line 27. The lines 26 and 27 are connected to a rectifier-filter supply (not shown in the diagram) incorporated in the enclosure 11. A resistor-capacitor filter 28 provides additional filtering, desirable for the amplifier stages which include the tubes V1 and V2. a

The control circuit16 comprises a grid-controlled gas discharge tube T1, an alarm relay .R1, and a time delay relay R2, all connected in series between the lines 26 and 27. The output of the amplifier 15 is coupled to the control grid 29 of the gas tube'Tl through a capacitor 30, and the control grid circuit is returned to the negative line 27 through a grid resistor 31. A cathode resistor 32 establishes a positive bias on the cathode 33 of the gas tube T1 and hence establishes the amplitude of signal voltage which must be applied to the control grid 29 to fire the tube T1. The cathode 33 and plate 34 of the negative bias upon the control grids of tubes V2 and V3 during an interval following the sounding of the loudspeaker. Thus the cathode 33 of the gas tube T1 has a small positive bias voltage, determined by the resistor 32 and resistors 39 and 40, when the tube is not conducting. However, when tube T1 fires, the voltage of the cathode 33 increases to a relatively high positive value and the capacitor 25 charges to that voltage (through the resistor 23). Then, when tube T1 again becomes non-conducting due to the opening of the contacts 37 and the cathode 33 returns to its original voltage, the voltage across the capacitor 25 is impressed,.as a high negative bias, upon the control grids of tubes V2 and V3. The

high negative bias efiectively blocks the amplifier stages 23 and 32 and into the capacitor 24. The value of resistube T1 constitute a series circuit with the resistor 32 and relays R1 and R2.

. The alarm relay R1 has normally-open contacts 37 thereof connected in a series circuit which includes terminal leads L1 and L2 and parallel branches comprising parallel branch including the time delay relay R2 and a variable resistor 38 (referred to as a reset circuit). When the tube T1 fires, the alarm relay R1 is energized and tor 23 is chosen so that thetime required to discharge capacitor 25 and bring the'voltage across the resistor'23 and capacitor 24 to the normal operating level inactivates the amplifier for the desired interval following the cessation of the alarm. In the embodiment of the invention described herein the cathode bias voltages were 8 volts and 98 volts; resistor 32, 10,000 ohms; capacitor 25, 4 mfd.; resistor 23, 1 megohrn; capacitor 24, l mfd.; and the discharge time was between 15 and 30 seconds. Ac-

cordingly, the amplifier 15 was inactive and the device did not respond to sounds, which would otherwise fire the contacts 37 are closed to activate the alarm circuit.' 7

With the terminal leads connected'to an alternating current line, activation of the alarm circuit will cause the' loudspeaker 17 to'be sounded. In testing or setting the T1 and activation ofthe alarm circuit. Thus, whenthe contacts 37 are closed, relay R2 is energized fromgthe power line (through the terminal leads L1 and L2) and,

' alarmv device, the switch S1 isopened and the indicator tube T1, for an interval of from 15 to 30 seconds follow ing'cessation of sounding of the speaker.

' The advantages of the arrangement will be apparent.

The device is made insensitive to echoes and vibrations caused by the loudspeaker and self-retripping is pre vented with a simple and efiicient control circuit 16.

The alarm device includes atest circuit for determining the performance or operability of the device, either duringinstallation orat any time thereafter. To this end a test switch S2 has a normally closed contact 41 con nected in the series cathode circuit of the gastube T1 and does not afi'ect the operation of that circuit. A normally open contact 42' is connected to the cathode 33 through a series resistor 43 such that, when the test following thedelay interval, the closed contacts of relay terruption of the series circuit causes the gas tube T1 to de-ionize, the circuit remains open until the gas tube T1 is again fired by an alarm signal of sufficient ampli tude. 1 U The relay R2 is a thermal time delay relay of-known the amplification control circuit may be tested at will and,

design and the variable resistor 38 provides adjustment V of the delay interval'to the desired'predetermined time.

Delay intervals of 30seconds are .useful in many applicationsof the' device and thejother known delaydevices may be utilized to obtainj'greater delay intervals or to Theterminal leads L1 and L2 are referredto as an switch is depressed, the resistor 43 is connected to the positive line 26 and the cathode 33 is energized to the same positive :voltage that it acquires when the tube T1 fires'in the ordinary operation of the control circuit, e.g1,- in the exemplary case, 98 volts. Upon release of the test switch, the voltage across the capacitor 25 is applied to inactivate the amplifier 15. With this arrangement,

further, the'alarm device may be inactivated for a time 1: sufi'icient to permit theuser to leave the room without trip ping the alarm, after the device has been set. 2

I potentiometer 44 in the grid circuit of tube V4 en- 7 ables adjustment. of 'the' amplifier 15 tov accommodate a ient pigs in the space undersurveillance and permits adjustment of the device to determine the magnitude of sound disturbance which will actuate the alarm.

The automatic sensitivity control circuit, indicated generally by the nurneral 60, functions to monitor the signal leaving the amplifieri15;to determine ifithe nature of it o r1g1n is environmental or intrusion.

the negative common line 27. The grid or base connecvtioni of tubefor amplifying means, V5 is connected tothe-variable or'center tap 66 of potentiometer 64. The

cathode or emitter side 68 of tube V5 is connected to the negative common line'27 through resistor 6 9.- The plate,

G collector, or output 70 of tube. V is connected to the positive line 26 through resistor 71. 'The plate or output 70 of tube V5 is also coupled to the cathode or emitter side 72 of diode tube or rectifying means V6 through capacitor '73. The cathode 72 of diode tube V6 is also connected to one side of a resistor 74, and the other side of resistor 74 is connected to the negative common line 27.

The plate, collector, or output 75 of tube V6 is con- .nected to one side of a resistor 76. The other side of resistor 76 is connected to the negative common line 27. The plate 75 of tube V6 is also connected to one side of capacitor 78. The other side of capacitor 78 is also connected to the negative common line 27. The plate 75 of tube V6 is further connected to one side of resistor 79. The other side of resistor 79 is connected through capacitor 30 to the negative common line 27 and is also connected to one side of another resistor 81. The second side of resistor 81 is conected to one side of a capacitor 82 and also to the grid feedbacks of tubes V2 and V3 in amplifier 15 through resistors 21 and 22, respectively. The second side of capacitor 82 is connected to the negative common line 27.

While it is theoretically possible for the automatic sensitivity control (hereinafter referred to as ASC) circuit 60 to monitor the signal at the plate of any of the tubes in the cascade amplifier circuit, it is more practical to monitor the signal as it leaves the last stage of the amplification in order to have the greatest signal strength available for operation of the ASC circuit.

The sensitivity of the ASC circuit 60 can be preset through the variable resistance of potentiometer 64, thus controlling the gain of the system through the grid voltage applied to tube V5. The tube V5 amplifies the signal received which passes through the rectifying tube V6, thus assuring that a negative voltage is always presented through the network of capacitors 7 8, 80 and 82, and resistors 76, 79 and 81. This network of capacitors and resistors provides a time delay barrier for the negative voltage leaving tube V6 before it is impressed as a negative bias on the grid returns of tubes V2 and V3 of the amplifier means 15.

in operation, the energizing circuit of the sound detection and alarm system requires the application of approximately six volts to the grid of the gas tube T1 to fire tube T1 and actuate the signaling means. Thus, if an intrusion sound is sufficient to create an impulse of six volts to the grid of tube T1 the alarm will be actuated.

However, let us suppose that a sporadic intrusion sound is detected by the system, as, for example, the approach of a train. It is apparent when the train is initially heard, the amplitude of the sound at the sound pickup location of the alarm system, will not be sufiicient to trigger the device, but will gradually or progressively increase in amplitude to a point which would be suificient to trigger the device. The electrical signal initiated by the sound of the train is monitored by the ASC circuit, and, because of the time delay feature of the ASC, will impress a negative bias on to the amplification circuit at a fixed interval of time after having been monitored.

A resistor 83 is connected between the capacitor 25 of the amplification control circuit and the ASC circuit to provide a high impedance to the biasing current of the ASC. In the embodiment shown, the use of a resistor 83 having a resistance of 560,000 ohms provides sufficient impedance to the ASC circuit and yet allows a fifteen second bias of the amplification circuit by the amplification control circuit. 7 i 7 Thus, the electrical signal resulting from an intrusion sound, such as the breaking of glass, or the like, will, because of the time delay in the ASC, fire tube T1 before the ASC biases the amplification circuit; whereas, a sound which progressively reaches the same amplitude will have warned the system of its impending arrival, permitting the ASC to have biased the amplifier circuit sufficiently to prevent theel'ectrical signal resulting from the sporadic environmental sounds from firing the gas tube T1 when the sound reaches triggering amplitude.

The time delay of the system can be varied by the value of the capacitors and resistors used in the time delay network, and it has been found that a delay of a few thousandths of a second is suificient and is eifected by employing 220,000 ohm resistors 79 and 81, 560,000 ohm resistor 76, and 0.1 mfd. capacitors 78, $0 and 82.

The values of the remaining resistors and capacitors used in the preferred embodiment of the ASC circuit are as follows: Cathode resistor 69, 560 ohms; cathode resistor 74, 560,000 ohms; plate to positive line resistor 71, 100,000 ohms; and capacitors 62 and 73, both 0.001 mfd.

The use of a 500,000 ohm potentiometer at in series with a 0.001 mfd. capacitor 62 not only controls the gain of the ASC circuit 60 but also prevents draining the signal leaving the amplifier completely away from the energizing circuit.

When the biasing voltage of the ASC circuit is impressed upon the grid returns of tubes V2 and V3, the voltage at the grid of gas tube T1 can be maintained at, say, a 5 volt level (i.e., one volt below firing) for any given environmental sound. It should be noted that even in the event that an intrusion sound occurs simultaneously with the environmental sound, the superimposed intrusion sound will increase the grid voltage of gas tube T1 to fire before the ASC can compensate for the increased signal leaving the amplifier.

Superimposed environmental sounds, however, will not actuate the system because the bias impressed by the ASC circuit will be increased proportionately to prevent the grid voltage on gas tube T1 from reaching firing potential. Thus, even if the train should blow its whistle, which, incidentally, emits a sound of gradually increasing amplitude, as it passes the surveillance area, the detection and alarm system will not be actuated.

it has also been found that if the detection and alarm system is in a building the ASC circuit will differentiate between sounds on the building walls and those exterior thereof. That is, if a bolt of lightning strikes ex'teriorly of the building, the sound dampening or attenuating barrier of the building itself will be sufiicient to permit the ASC to operate and prevent actuation of the alarm.

It is, therefore, apparent that a sound actuated detection and alarm system constructed in accordance with the concept herein disclosed accomplishes the objects of the invention.

What is claimed is:

In a sound actuated detection and alarm device having sound pickup means, first amplifier means having the input thereof connected to said sound pickup means, at least one signaling device and an energizing circuit actuated by said first amplifier means for triggering said signaling device, said energizing circuit having thermal delay deactuating means and amplification control time delay feedback means, the improvement comprising; second amplifier means having the grid control input thereof connected to the output of said first amplifier means through a potentiometer having a resistance of on the order of 5'00,000 ohms to prevent excessive draining of the signal from said first amplifier means, rectifier means connected to the output of said second amplifier means, a timedelay network connecting said rectifier means to said first amplifier means ahead of the output thereof to impress a negative blocking bias thereto delayed by a few milliseconds to prevent said first amplifier means from triggering said energizing circuit in response to environmental sounds, and a high impedance blocking means connected between said time-delay network and said amplification control time-delay feedback means to prevent impressing signals from said time-delay network on said. energizing circuit.

(References on following page) References Cited by the Examil ler 2,799,737 7/57' Rich 330-441 UNITED STATES PATENTS 2,832,915 4/58 NICCOY 340-261 2,903,683 9/59 Bagno 340 25s 5:221:23 fEFELIII: 331L123) 2,960,661 11/60 Bratschi X 12/42 Groenendyke 330 141 5 2,987,713 6/61 B ---r 249-258 9/43 Wellehstien et a1. 330 141 3,049,699 8/162 m k et 97- t 33 4 1 9 V I 1 117:3 340 1 5.; FOREIGN PATENTS 5/55 Schmidt 340 25s 10 604,499 7/48 Great Britain.

1/56 De Boisblanc.

6/56 London et a1 0 2 NEIL C. READ, Przmary Exammer. 

